20 General utilities library [utilities] (original) (raw)
20.14 Function objects [function.objects]
20.14.8 Comparisons [comparisons]
20.14.8.1 General [comparisons.general]
The library provides basic function object classes for all of the comparison operators in the language ([expr.rel], [expr.eq]).
For templates less, greater, less_equal, andgreater_equal, the specializations for any pointer type yield a result consistent with the implementation-defined strict total order over pointers ([defns.order.ptr]).
[Note 1:
If a < b is well-defined for pointers a and b of type P, then (a < b) == less<P>()(a, b),(a > b) == greater<P>()(a, b), and so forth.
— _end note_]
For template specializations less<void>, greater<void>,less_equal<void>, and greater_equal<void>, if the call operator calls a built-in operator comparing pointers, the call operator yields a result consistent with the implementation-defined strict total order over pointers.
20.14.8.2 Class template equal_to [comparisons.equal.to]
template<class T = void> struct equal_to { constexpr bool operator()(const T& x, const T& y) const;};
constexpr bool operator()(const T& x, const T& y) const;
template<> struct equal_to<void> { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) == std::forward<U>(u));using is_transparent = _unspecified_;};
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) == std::forward<U>(u));
Returns: std::forward<T>(t) == std::forward<U>(u).
20.14.8.3 Class template not_equal_to [comparisons.not.equal.to]
template<class T = void> struct not_equal_to { constexpr bool operator()(const T& x, const T& y) const;};
constexpr bool operator()(const T& x, const T& y) const;
template<> struct not_equal_to<void> { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) != std::forward<U>(u));using is_transparent = _unspecified_;};
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) != std::forward<U>(u));
Returns: std::forward<T>(t) != std::forward<U>(u).
20.14.8.4 Class template greater [comparisons.greater]
template<class T = void> struct greater { constexpr bool operator()(const T& x, const T& y) const;};
constexpr bool operator()(const T& x, const T& y) const;
template<> struct greater<void> { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) > std::forward<U>(u));using is_transparent = _unspecified_;};
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) > std::forward<U>(u));
Returns: std::forward<T>(t) > std::forward<U>(u).
20.14.8.5 Class template less [comparisons.less]
template<class T = void> struct less { constexpr bool operator()(const T& x, const T& y) const;};
constexpr bool operator()(const T& x, const T& y) const;
template<> struct less<void> { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) < std::forward<U>(u));using is_transparent = _unspecified_;};
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) < std::forward<U>(u));
Returns: std::forward<T>(t) < std::forward<U>(u).
20.14.8.6 Class template greater_equal [comparisons.greater.equal]
template<class T = void> struct greater_equal { constexpr bool operator()(const T& x, const T& y) const;};
constexpr bool operator()(const T& x, const T& y) const;
template<> struct greater_equal<void> { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) >= std::forward<U>(u));using is_transparent = _unspecified_;};
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) >= std::forward<U>(u));
Returns: std::forward<T>(t) >= std::forward<U>(u).
20.14.8.7 Class template less_equal [comparisons.less.equal]
template<class T = void> struct less_equal { constexpr bool operator()(const T& x, const T& y) const;};
constexpr bool operator()(const T& x, const T& y) const;
template<> struct less_equal<void> { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) <= std::forward<U>(u));using is_transparent = _unspecified_;};
template<class T, class U> constexpr auto operator()(T&& t, U&& u) const -> decltype(std::forward<T>(t) <= std::forward<U>(u));
Returns: std::forward<T>(t) <= std::forward<U>(u).
20.14.8.8 Class compare_three_way [comparisons.three.way]
In this subclause, BUILTIN-PTR-THREE-WAY(T, U)for types T and U is a boolean constant expression.
BUILTIN-PTR-THREE-WAY(T, U) is trueif and only if <=> in the expressiondeclval<T>() <=> declval<U>() resolves to a built-in operator comparing pointers.
struct compare_three_way { template<class T, class U> requires three_way_comparable_with<T, U> || BUILTIN-PTR-THREE-WAY(T, U) constexpr auto operator()(T&& t, U&& u) const;using is_transparent = unspecified;};
template<class T, class U> requires three_way_comparable_with<T, U> || _BUILTIN-PTR-THREE-WAY_(T, U) constexpr auto operator()(T&& t, U&& u) const;
Preconditions: If the expression std::forward<T>(t) <=> std::forward<U>(u) results in a call to a built-in operator <=> comparing pointers of type P, the conversion sequences from both T and U to Pare equality-preserving ([concepts.equality]).
Effects:
- If the expression std::forward<T>(t) <=> std::forward<U>(u) results in a call to a built-in operator <=> comparing pointers of type P, returns strong_ordering::less if (the converted value of) t precedes u in the implementation-defined strict total order over pointers ([defns.order.ptr]),strong_ordering::greater if u precedes t, and otherwise strong_ordering::equal.
- Otherwise, equivalent to: return std::forward<T>(t) <=> std::forward<U>(u);